A common and frequently disabling knee injury sustained in sporting activities is a tear of the anterior cruciate ligament (ACL). The choice of treatment remains a dilemma. Ligament repair and/or reconstruction seldom return the knee to normal function, involve a year or more rehabilitation period and have a significant failure and complication rate. Which patients should be repaired and/or reconstructed and which patients should be managed without ligament surgery? What is the fate of the ACL disrupted knee? What is the level of disability after an ACL injury? What factors correlate with disability, repeated injury and joint deterioration: age, sex, joint laxity, associated joint pathology, sports participation, etc.? Between June of 1981 and July of 1986 we entered three hundred and eighty-seven patients into a "Fate of the ACL Injured Knee" study. All patients included in the study presented with their first knee injury within fourteen days of the injury event, had a hemarthrosis and were suspected of being an ACL injury. Two hundred and seventy-two of the patients had sustained an anterior cruciate ligament tear. The initial evaluation included A/P instrumented laxity examination with the MedMetric KT1000 knee ligament arthrometer. Two hundred and fifty of the patients (73%) had an arthroscopic examination. Sixty-three of the patients had an anterior cruciate ligament reconstruction within month of injury. We propose to perform follow-up evaluations on all patients in the "Fate of the ACL Injuried knee" study. The evaluation will document the patients' level of sports participation, functional problems in sports, work, and activities of daily living, brace use, and incidence of subsequent knee injury and surgery. Anterior/posterior joint laxity will be measured. Quantifiable functional knee tests will be performed Radiographic evaluation and radionuclide imaging of the knee will be used to document joint pathology. The objective of the study is to characterize the fate of the ACL injuried knee, with and without ligament surgery, and to identify factors that place the patient at risk of further knee injury and deterioration if not reconstructed.